No abstract

No abstract

Glyceric acid (GA), an unfamiliar biotechnological product, is currently produced as a small by-product of dihydroxyacetone production from glycerol by Gluconobacter oxydans. We developed a method for the efficient biotechnological production of GA as a target compound for new surplus glycerol applications in the biodiesel and oleochemical industries. We investigated the ability of 162 acetic acid bacterial strains to produce GA from glycerol and found that the patterns of productivity and enantiomeric GA compositions obtained from several strains differed significantly. The growth parameters of two different strain types, Gluconobacter frateurii NBRC103465 and Acetobacter tropicalis NBRC16470, were optimized using a jar fermentor. G. frateurii accumulated 136.5 g/liter of GA with a 72% D-GA enantiomeric excess (ee) in the culture broth, whereas A. tropicalis produced 101.8 g/liter of D-GA with a 99% ee. The 136.5 g/liter of glycerate in the culture broth was concentrated to 236.5 g/liter by desalting electrodialysis during the 140-min operating time, and then, from 50 ml of the concentrated solution, 9.35 g of GA calcium salt was obtained by crystallization. Gene disruption analysis using G. oxydans IFO12528 revealed that the membrane-bound alcohol dehydrogenase (mADH)-encoding gene (adhA) is required for GA production, and purified mADH from G. oxydans IFO12528 catalyzed the oxidation of glycerol. These results strongly suggest that mADH is involved in GA production by acetic acid bacteria. We propose that GA is potentially mass producible from glycerol feedstock by a biotechnological process.

Self-assembling properties of "natural" glycolipid biosurfactants, mannosyl-erythritol lipids A and B (MEL-A, MEL-B), which are abundantly produced from yeast strains, were investigated by using the fluorescence-probe method, dynamic light-scattering (DLS) analysis, freeze-fracture transmission electron microscopy (FF-TEM), and synchrotron small/wide-angle X-ray scattering (SAXS/WAXS) analysis, among other methods. Both MEL-A and MEL-B exhibit excellent self-assembly properties at extremely low concentrations; they self-assemble into large unilamellar vesicles (LUV) just above their critical-aggregation concentration (CAC). The CAC(I) value was found to be 4.0x10(-6) M for MEL-A and 6.0x10(-6) M for MEL-B. Moreover, the self-assembled structure of MEL-A above a CAC(II) value of 2.0x10(-5) M was found to drastically change into sponge structures (L3) composed of a network of randomly connected bilayers that are usually obtained from a complicated multicomponent "synthetic" surfactant system. Interestingly, the average water-channel diameter of the sponge structure was 100 nm. This is relatively large compared with those obtained from "synthetic" surfactant systems. In addition, MEL-B, which has a hydroxyl group at the C-4' position on mannose instead of an acetyl group, gives only one CAC; the self-assembled structure of MEL-B seems to gradually move from LUV to multilamellar vesicles (MLV) with lattice constants of 4.4 nm, depending on the concentration. Furthermore, the lyotropic-liquid-crystal-phase observation at high concentrations demonstrates the formation of an inverted hexagonal phase (H2) for MEL-A, together with a lamella phase (L(alpha)) for MEL-B, indicating a difference between MEL-A and MEL-B molecules in the spontaneous curvature of the assemblies. These results clearly show that the difference in spontaneous curvature caused by the single acetyl group on the head group probably decides the direction of self-assembly of glycolipid biosurfactants. The unique and complex molecular structures with several chiral centers that are molecularly engineered by microorganisms must have led to the sophisticated self-assembling properties of the glycolipid biosurfactants.

Coacervate (L3 phase) formation of the single component "natural" glycoliped biosurfactant, MEL-A, was observed for the first time by using an optical microscope, a confocal laser scanning microscope (CLSM), and a freeze-fracture electron microscope (FF-TEM). It was also found that only a slight decrease in spontaneous curvature resulting from the absence of one acetyl group on the headgroup induced a drastic morphological change in the 3D self-assembled structure from coacervates (L3 phase) to ordered vesicles (Lalpha phase).

A coupled fermentation/pervaporation process for reliable production of concentrated ethanol was studied using ethanol permselective silicalite membranes coated with two types of silicone rubber, KE-45 and KE-108, as a hydrophobic material. Ethanol recovery was greatly improved by using a membrane coated with KE-45 silicone rubber. The recovered ethanol concentration in the permeate was 67% (w/w), and the amount of recovered ethanol from the broth was more than 10 times higher than that using a noncoated membrane. Succinic acid and glycerol, by-products created during fermentation, interfered with the pervaporation performance of the coated membrane when used to separate an ethanol/water solution.

No abstract

This study aims to explore the structural characteristics of the inhomogeneous top layer of thin-film composite membranes when pretreated by different methods: room temperature−oven, ethanol−hexane in a solvent exchange process, and freeze-drying. An evaluation of the nano-order free-volume pore size of the polyamide samples was carried out by nanopermporometry (NPP) and was quantitatively compared with the free-volume pore estimated from normalized Knudsenbased permeance (NKP) and with positron annihilation characterization (PALS). NPP results denoted a bimodal polyamide membrane structure described by a dense matrix and highly permeable regions. The application of different condensable vapors (water, hexane, and isopropanol) resulted in a free-volume pore size smaller than d p = 0.6 nm for dense regions, which was confirmed after NKP and PALS. In addition, the influence of highly permeable regions on permeance decreased in the following order: ethanol−hexane > freeze-drying > room temperature−oven samples, demonstrating an effective membrane structure alteration after different pretreatments.